Molecular Genetics of Amino Acid Biosynthesis in Arabidopsis

通过对拟南芥耐旱突变体eir1和eir1基因的分析表明，该突变体是由极性输运模型预测的泵。仅在植物根部表达的EIR1蛋白与一些细菌外排泵有相似之处。实验将为EIR1在极性输运中的作用提供直接证据。EIR1基因增强和抑制外排的突变体将在酵母中产生，这一系统为探索植物中的这一途径提供了独特的工具。运输实验将测量吲哚类化合物在酵母中的直接外排。通过确定EIR1在根细胞质膜中是否存在不对称定位，来检验EIR1在吲哚乙酸（IAA）从根尖向伸长区不对称运输中的作用。筛选eir1的抑制子和增强子应该能识别出转导倾斜性信号的上游和下游基因。对EIR相似物的其他家族成员的分子分析将确定这些是否是IAA泵负责生长素对其他组织趋向性的影响。这些基因将被克隆，并在这些EIR1类似物中含有显性负突变的转基因植物（在酵母试验中验证），将用于构建转基因植物，然后分析其趋向性缺陷。利用从筛选中获得的突变体，构建细胞扩增的遗传途径。其他旨在描述侧根形成途径的实验包括克隆编码ALF4的基因。af1突变体可以通过内源和外源IAA阻断侧根的形成。此外，本文还提出了一种新的抗高盐转基因植物的设计方法。本研究的目的是确定植物激素生长素（IAA）促进植物趋向性的信号转导途径。在地心引力说中，根向地心弯曲。极性输运假说假设有一个外排转运体将IAA从根尖泵到最靠近地球中心的根部。在那里，IAA抑制细胞的伸长，而另一边的细胞则伸长，结果是根向下弯曲，向那个方向生长。

Analysis of the agravitropic mutant of Arabidopsis thaliana, eir1 and the EIR1 gene, suggests that it is the pump predicted by the polar transport model. The EIR1 protein, expressed only in the root of the plant has similarities to some bacterial efflux pumps. Experiments to provide direct evidence for the function of EIR1 in polar transport will be done. Mutants of the EIR1 gene that enhance and inhibit efflux will be generated in yeast, a system which provides a unique tool to probe this pathway in plants. Transport experiments will measure the efflux of indolic compounds directly in yeast. The role of EIR1 in asymmetric transport of indol acetic acid (IAA) from the root tip to the elongation zone will be tested by determining whether there is asymmetric localization of EIR1 in the plasma membrane of root cells. Genetic screens for suppressors and enhancers of eir1 should identify the upstream and downstream genes that transduce the signal for gravitropism. Molecular analysis of the other family members of EIR paralogs will determine whether these are the IAA pumps responsible for the effects of auxin on tropisms in other tissues. These genes will be cloned and transgenic plants containing dominant negative mutations in these EIR1 paralogs (validated in a yeast assay), will be used to construct transgenic plants, which will then be analyzed for tropism defects. A genetic pathway for cell expansion will be constructed using mutants obtained from a screen, which has been developed. Other experiments designed to delineate the pathway of lateral root formation involve cloning the gene encoding ALF4. af1 mutants block lateral root formation both by endogenous and exogenous IAA. In addition, a novel approach is described to engineer transgenic plants resistant to high salt.The goal of this work is to identify the signal transduction pathway(s) by which the plant hormone auxin (or IAA) promote plant tropisms. In gravitropism, the root bends towards the center of the earth. The polar transport hypothesis posits an efflux transporter that pumps IAA up from the root tip to the side of the root closest to the center of the earth. There the IAA inhibits the elongation of the cells, whereas those on the opposite side elongate, with the result that the root bends down and grows in that direction.